Optical glass

ABSTRACT

An optical glass having a high index of refraction, a low dispersion, and low color, consists essentially of lanthanum oxide (La2O3), thorium dioxide (ThO2), tantalum pentoxide (Ta2O5), boric oxide (B2O3), silicon dioxide (SiO2), and germanium dioxide (GeO2).

United States Patent 1 1 1] 3,715,221

Greco 1 1 Feb, 6, 1973 41 OPTICAL GLASS 3,150,990 9/1964 Faulstich..l06/47 Q Inventor: Edgar J. Greco, Rochester N.Y 3,563,773 2/1971Bromer et al ..106/54 [73] Assigneez Eastman Kodak Company, FOREIGNPATENTS OR APPLICATIONS Rochester, NY. 1,109,698 4/1968 Great Britain..l06/47 Q [22] Filed: Jan. 1971 Primary ExaminerWinston A. Douglas [21]Appl. No.: 111,113 Assistant ExaminerM Bell Att0rneyW. H. J. Kline andD. Peter Hochberg [52] US. Cl ..106/47 Q, 106/54 [57] ABSTRACT [51] Int.Cl. .C03c 3/12, C030 3/30, C03c 3/00 58 Field 61 Search ..l06/47 Q, 54An Optical glass having a g index of refraction, a low dispersion, andlow color, consists essentially of [56] References Cited lanthanum oxide(M1 0 thorium dioxide (ThO tantalum pentoxide (T21 0 boric oxide (B 0sil- UNITED STATES PATENTS icon dioxide (SiO- and germanium dioxide (GeO2,787,554 4/1957 De Paolis ..l06/47 Q 10 Claims, No Drawings OPTICALGLASS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to optical glasses, and in par- 5 ticular to opticalglasses having high refractive indices, low dispersions and low color.

2. Description of the Prior Art It is well known in the glass and lensmaking arts that optical glasses having high indices of refraction andlow dispersions (i.e. optical crown glasses) find great utility in lenssystems. Glasses with high indices of refraction are desirable becausethey reduce the required curvature of the lens elements made from theglass, and thereby make possible the manufacture of many other- 1 wiseimpractical lens systems. However, the development of optical glasseshaving very high refractive indices (i.e. where the index approaches andexceeds 1.90) has been severely impeded by the tendency of such glassesto exhibit a high color i.e. these glasses exhibit undesirably highabsorption in the visible region ofthe spectrum.

For example, US. Pat. No. 3,150,990 which issued on Sept. 29, 1964teaches a relatively" colorless high index glass having a high contentof La O ThO and Ta O and at least 2 percent by weight of niobiumpentoxide (Nb O The patent correctly points out that previous high indexglasses were characterized by their high content of titanic oxide (TiOwhich gave to the glass a yellow-brown color. However, it has been foundthat the very ingredient which the patentee of the cited patent findsessential to the achievement of the high index qualities attributed tohis glass (as elaborated upon in a paper entitled Mehrstoffsysteme zumAufban optischer Glaser. Teil ll: System B La O ThO Ta O Nb O which waspublished in Glatechnische Berichte 34 (No. 3): 102-107, in March 1961)is itself a source of objectionably high color. As is explained below,the present invention provides a high index crown glass having extremelylow color, which is achieved at least in part by he absenceof Nb,O

SUMMARY OF THE INVENTION An object of the present invention is toprovide an optical glass having a high index of refraction, a lowdispersion, and low color.

Another object is to provide a glass having the aforementionedcharacteristics, which can be produced under practicable manufacturingconditions in an economical manner.

Other objects will be apparent to those skilled in the art, from thedescription to follow and from the appended claims.

These objects are achieved by the provision of the Component WeightPercent lanthanum oxide (La,O 15-30 thorium dioxide (ThO,) 20-45tantalum pentoxide (Ta,O 24-40 boric oxide (8,0,) 4-10 silicon dioxide(SiO,)

germanium dioxide (GeO,)

In addition to the foregoing components, the following components can beadded within the specified ranges of weight percentages to achieveglasses exhibiting the desired characteristics:

Component Weight Percent zirconium dioxide (ZrO 0-10 titanium dioxide(TiO,) O-5 bismuth trioxide (Bi O 0-5 lead monoxide (PbO) 0-6 potassiummonoxide (K 0) 0-2- barium oxide (BaO) 0-5 zinc oxide (ZnO) 0-5 arsenictrioxide (As O 0-2 DETAlLED DESCRIPTION OF THE PREFERRED EMBODIMENTS Thepresent invention provides optical glasses having refractive indices (nof 1.90 and above, low dispersions with Abbe numbers (V within the rangeof 30-40, and extremely low color. These glasses belong to the system B0 La O ThO Ta O with a partial'substitution of SiO and GeO for B 0 Thus,a. combination of glass formers (B 0 SiO and GeO rather than the soleuse of B 0 enables the development of colorless, high index glasses. Thelow color of the present glasses has been attributed to the virtualabsence of Nb O and TiO The excellent optical properties of theseglasses appears to be due to the substantial exclusion of divalent metalions, which are used in other glasses for the purpose of improvingstability (at the expense of the optical properties of the glass).Slight amounts only of the following components having divalent metalions are included in the glasses of the present invention:

barium oxide (BaO) zinc oxide (ZnO) cadmium oxide (CdO) The foregoingcomponents are not necessary for these glasses, but their addition hasin some instances proven advantageous.

The following glasses, which were melted in platinum crucibles in atemperature range of 1340 to 1550C, are characterized by especially highindices of refraction:

WEIGHT PERCENT OF EACH COMPONENT Example No. B 0 S101 (i003 1.18.103Th0; T3305 'IiO B1203 B110 Zrm PM) ll]; vn

J. 00 2. 4. 50 26. 10 25. 20 36. 7 w. 00 2. 55 4. 25 24. 66 23. 81 31.'0 1.00 2. 55 4. 25 24. 66 23. 81 35. l J. ()0 2. 41 4. 00 23. 21 32. 4337. i 1). 00 2. 26 3. 21. 31. 04 30. A J. 00 1. 81 3. 01 2O. 41! 25.8'.) 18 34. 8 4. O0 8. 52 4. 20 24. 38 23. 54 .35 38. 2 J. 60 4. 23 1.21 20. 86 26. 41 .24. 16 1. 45 6. 70 5. 38 1. 34. 4

present invention of optical glasses consisting essen-- tially ofcomponents in the following ranges of percentages by weight:

The components of these especially advantageous glasses fall within thefollowing ranges of weight percentages:

Component Weight Percent 820:: 4-l 000 1 -6 L8 0. 1 6-27 ThO 23-4 1 T30. 24-40 T 0-5 ai o 0-5 BaO 0-5 ZrO 0-7 PbO 0-6 Up to two percent byweight of arsenic trioxide (AS203) can be added to any of the aboveglass compositions as a clarifier.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

Iclaim:

1. Optical glasses having a refractive index in the range from 1.90 to2.00 and an Abbe number in the range from 30.0 to 40.0, said glassesbeing free of Nbzos and consisting essentially of components in thefollowing ranges of percentages by weight:

Component Percentage lanthanum oxide (La O -30 thorium dioxide (ThO -45tantalum pentoxide (Ta O 24-40 borie oxide (B 0 4-10 silicon dioxide(SiO 1-9 germanium dioxide (GeO 1-6 2. Optical glasses having arefractive index in the range from 1.90 to 2.00 and an Abbe number inthe range from 30.0 to 40.0, said glasses being free of Nb O andconsisting essentially of components in the following ranges ofpercentages by weight:

Component Weight Percent boric oxide (B 0 4-10 silicon dioxide (SiO l-9germanium dioxide (GeO 1-6 lanthanum oxide (La 0 16-27 thorium dioxide(ThO 23-41 tantalum pentoxide (Ta O 24-40 titanic oxide (TiO 0-5 bismuthtrioxide (Bi O 0-5 barium oxide (BaO) 0-5 zirconium oxide (ZrO 0-7 leadmonoxide (PbO) 0-6 arsenic trioxide (AS203) 0-2 3. An optical glassaccording to claim 2 having the following composition by weight:

Component Weight Percent B 0 9.00 SiO 2.70 01:0 4.50 La o; 26.10 Th0;25.20 Ta,0,, 32.50

4. An optical glass according to claim 2 having the followingcomposition by weight:

Component Weight Percent B 0 9.00 SiO, 2.55 GeO 4.25 La O 24.66

no, 23.81 Ta,O 30.71 'no 5.00

5. An optical glass according to claim 2 having the followingcomposition by weight:

Component Weight Percent a 9.00 SiO, 2.55 GeO, 4.25 La O 24.66 Th0,23.81 T8105 30.71 Bi O 5.00

6. An optical glass according to claim 2 having the 7. An optical glassaccording to claim 2 having the following composition by weight:

Composition Weight Percent 0 9.00 SiO 2.26 GeO, 3.75 1521 0 21.80 'lhO31.04 Ta O 32.14

8. An optical glass according to claim 2 having the followingcomposition by weight:

Composition Weight Percent a 9.00 2 1.81 GeO 3.01 La 0 20.49 Th0: 25.89Ta O, 39.78

9. An optical glass according to claim 2 having the followingcomposition by weight:

Composition Weight Percent B 0 4.00

z 8.52 GeO 4.20 La,0, 24.38 Th0, 23.54 T8405 30.35 8210 5.00

10. An optical glass according to claim 2 having the followingcomposition by weight:

Composition Weight Percent B 0 9.60 S10 4.23 GeO, 1.21 La O, 20.86 Th0,26.41 Ta O 24.16 ZrO, 6.70 PbO 5.38 TiO1 1.45

1. Optical glasses having a refractive index in the range from 1.90 to2.00 and an Abbe number in the range from 30.0 to 40.0, said glassesbeing free of Nb2O5 and consisting essentially of components in thefollowing ranges of percentages by weight: Component Percentagelanthanum oxide (La2O3) 15-30 thorium dioxide (ThO2) 20-45 tantalumpentoxide (Ta2O5) 24-40 boric oxide (B2O3) 4-10 silicon dioxide (SiO2)1-9 germanium dioxide (GeO2) 1-6
 2. Optical glasses having a refractiveindex in the range from 1.90 to 2.00 and an Abbe number in the rangefrom 30.0 to 40.0, said glasses being free of Nb2O5 and consistingessentially of components in the following ranges of percentages byweight: Component Weight Percent boric oxide (B2O3) 4-10 silicon dioxide(SiO2) 1-9 germanium dioxide (GeO2) 1-6 lanthanum oxide (La2O3) 16-27thorium dioxide (ThO2) 23-41 tantalum pentoxide (Ta2O5) 24-40 titanicoxide (TiO2) 0-5 bismuth trioxide (Bi2O3) 0-5 barium oxide (BaO) 0-5zirconium oxide (ZrO2) 0-7 lead monoxide (PbO) 0-6 arsenic trioxide(As2O3) 0-2
 3. An optical glass according to claim 2 having thefollowing composition by weight: Component Weight Percent B2O3 9.00 SiO22.70 GeO2 4.50 La2O3 26.10 ThO2 25.20 Ta2O5 32.50
 4. An optical glassaccording to claim 2 having the following composition by weight:Component Weight Percent B2O3 9.00 SiO2 2.55 GeO2 4.25 La2O3 24.66 ThO223.81 Ta2O5 30.71 TiO2 5.00
 5. An optical glass according to claim 2having the following composition by weight: Component Weight PercentB2O3 9.00 SiO2 2.55 GeO2 4.25 La2O3 24.66 ThO2 23.81 Ta2O5 30.71 Bi2O35.00
 6. An optical glass according to claim 2 having the followingcomposition by weight: Component Weight Percent B2O3 9.00 SiO2 2.41 GeO24.00 La2O3 23.21 ThO2 32.43 Ta2O5 28.92
 7. An optical glass according toclaim 2 having the following composition by weight: Composition WeightPercent B2O3 9.00 SiO2 2.26 GeO2 3.75 La2O3 21.80 ThO2 31.04 Ta2O5 32.148. An optical glass according to claim 2 having the followingcomposition by weight: Composition Weight Percent B2O3 9.00 SiO2 1.81GeO2 3.01 La2O3 20.49 ThO2 25.89 Ta2O5 39.78
 9. An optical glassaccording to claim 2 having the following composition by weight:Composition Weight Percent B2O3 4.00 SiO2 8.52 GeO2 4.20 La2O3 24.38ThO2 23.54 Ta2O5 30.35 BaO 5.00